In many optical systems, it is necessary to gather light from very distant scenes at oblique viewing angles through the atmosphere. These systems include ground-based telescopes which view astronomical objects as well as airborne or space-borne surveillance systems which monitor the ground.
As the light travels through the atmosphere, it is spectrally dispersed. This spectral dispersion can have negative effects on the operation of the optical system. It is desirable to sense the amount of dispersion introduced by the atmosphere so that the dispersion, and thus its deleterious effects on the optical system, can be compensated.